The invention relates to a relay, in particular a micro-relay, comprising a bridge-type make contact. In addition thereto, the invention relates to a method of making the relay.
The document DE 44 37 261 C1 discloses a micro-relay adapted to be produced micromechanically, consisting of an etched-free silicon spring tongue, which is pre-curved, and of a planar counter-electrode. The spring tongue constitutes a wedge-shaped capacitor together with the counter-electrode. By application of a control voltage between spring tongue and planar counter-electrode, the spring tongue is stretched until the free spring end touches the working contact on the counter-electrode. During the switching operation, the curved spring tongue rolls on the counter-electrode and thus forms a migrating wedge.
In addition to relays having a single closer or make contact function, in which the load current to be switched is conducted in a conductive track on the movable spring, there are desirable relays in which a make contact constitutes a bridging contact across two fixed contacts. The bridge-type make contact offers higher voltage strength and, in case of high-frequency load current signals, a lower crosstalk capacity and thus higher frequency response. However, with bridge-type make contacts, there is the problem that the fixed contacts may be subject to wear to different extents, thereby making the switching strokes of the individual fixed contacts different from each other. The result of this is that there are different contact forces arising at the two fixed contacts. Strong wear on one side would have the effect that one contact in the end would no longer close at all.
For realizing a bridge-type make contact with the aid of the known micro-relay, the movable spring tongue would have a rectangular contact arranged thereon, covering two fixed counter-contacts. Such an arrangement has the disadvantage that different contact forces arise in case of different wear of the two juxtaposed fixed contacts. Due to the high torsional rigidity of the spring tongue, the bridge contact cannot adjust to counter-contacts of different heights. In case of a further increasing difference in height, one contact finally would no longer be closed at all.
It is thus the object of the present invention to make available a relay which is adapted to be miniaturized and which establishes safe bridging contact also in case of different heights of the fixed contacts. The invention furthermore relates to a method of making the micro-relay. This object is met according to the invention by a relay according to claim 1. Advantageous developments of the invention and a method of making the invention are indicated in the further claims.
The invention indicates a relay comprising a base member with two fixed contacts as well as a switching spring. The switching spring is attached by way of an edge portion along a mounting line and is movable between two positions, an open one and a closed one. In addition thereto, the switching spring has a contact spring. Arranged on the contact spring is a movable contact bridging the fixed contacts when the switching spring is in the closed position. Furthermore, the relay comprises a drive member moving the switching spring and the contact spring between the open and closed positions. The contact spring is in the form of a torsion spring that is rotatable about an axis of rotation. The axis of rotation is located in the plane of the contact spring in the middle between the two fixed contacts. The projection of the axis of rotation onto the base member intersects the connecting line of the fixed contacts substantially at right angles.
The effect achievable by the splitting of the relay spring into a contact spring and a switching spring, according to the invention, with the contact spring being in the form of a torsion spring, is that safe contact is guaranteed also with different heights of the fixed contacts. Due to the rotatability of the torsion spring about an axis of rotation between the fixed contacts, the movable contact can adjust to different heights of the fixed contacts. This is possible without impairing the switching behavior of the switching spring.
Especially easy miniaturization is obtained with a relay according to the invention in which the contact spring is part of the switching spring.
The contact spring, in particularly advantageous manner, can be made from the switching spring in that portions of the switching spring are etched away. Such a procedure in particular provides for the possibility of utilizing the patterning techniques known from silicon technology, with these being possibly transferred to a metallic switching spring.
A contact spring that is rotatable about an axis of rotation is attained in particularly simple and thus advantageous manner by providing a contact part and one or more spring parts in the contact spring. The contact part constitutes the carrier of the movable contact and extends transversely of the axis of rotation so as to cover the fixed contacts. This contact part is connected to the switching spring by one or more spring parts, with the spring parts being connected to the contact part in the region of the axis of rotation of the torsion spring. The effect achieved thereby is that the contact spring is a torsion spring and at the same time is resiliently coupled to the switching spring.
In addition thereto, a development of the relay according to the invention is particularly advantageous in which the shape of the spring parts follows multiply curved paths. Due to this extended spring path, it is possible in particularly simple manner to obtain an arbitrary low rigidity of the torsion spring, which facilitates tilting of the movable contact so as to abut on two fixed contacts of different heights.
Furthermore, it is particularly advantageous to arrange the spring parts on two opposite sides of the switching part, thereby ensuring that the axis of rotation is not tilted due to unilateral mounting of the contact part.
Moreover, it is particularly advantageous to design the relay in a manner in which the switching spring is attached to the base member and is curved away from the same. This renders possible the realization of a relay comprising a bridge contact with the initially indicated migrating wedge.
With this arrangement (with curved switching spring), it is particularly advantageous when the connecting line between the fixed contacts is parallel to the mounting line. Due to the fact that the switching spring, in case of a relay making use of the migrating wedge principle, is urged onto a counter-piece starting from the mounting line, the effect achieved by equal distances of the fixed contacts from the mounting line is that the movable contact contacts the fixed contacts almost simultaneously. For the same reason, such a relay employing this arrangement of the fixed contacts, at all times has the same contact distances between the fixed contacts and the movable contact.
It is particularly advantageous to choose an electrostatic drive as drive member for the relay. Such a drive consists in that a first electrode, arranged on the side of the switching spring facing the base member, and a second electrode, arranged on the base member opposite the first electrode, are connected to a dc voltage source. Such a drive requires energy for switching for short times only, whereas the closed position is fixed solely by electrostatic interaction, without necessitating the supply of additional energy.
In addition thereto, a relay is particularly advantageous in which the switching spring consists of silicon and the base member consists of silicon or glass. Such a relay can be realized easily with the structuring or patterning and manufacturing techniques known from silicon technology.
The invention furthermore indicates a method of making such a relay, comprising the following steps:
1. The second electrode and the fixed contacts are deposited on the base substrate constituting the base member and then are patterned.
2. Thereafter, an insulating layer is deposited on the second electrode.
3. A silicon wafer having a doped silicon layer on the side of the wafer facing the base substrate is bonded onto the base substrate.
4. Beginning from the side of the silicon wafer facing away from the doped silicon layer, said wafer is etched back, e.g. by KOH etching, until the doped silicon layer is left standing that is to form the switching spring.
5. Finally, by patterning of the doped silicon layer, the contact spring is formed from the switching spring or the switching spring itself is formed, respectively.
Such a method has the advantage that miniaturized relays can be manufactured very easily.